In the fabrication of glass articles, batch material is reduced to molten glass by passing the batch material through a melting furnace, which is commonly referred to as a melter. The molten glass is delivered downstream from the melter through a system of channels and forehearths. This system of channels and forehearths is referred to as a front end. The front end serves as a conduit to deliver the molten glass to one or more production points. The front end also serves to cool and condition the molten glass prior to reaching the production points. These production points are referred to as forming positions. Each forming position includes a bushing for a fiber forming operation or a gob cutter for a container forming operation. Bushings or gob cutters typically are secured to the forehearths via forehearth steel.
maintain the molten glass G at a desired operational temperature. An example of a conventional forehearth 10 is shown in FIG. 1. The forehearth 10 includes a top or crown (not shown), a bottom (also not shown), and laterally spaced sidewalls 16. Portions of the forehearth 10 above the level of the molten glass G are constructed of super structure refractory. Portions of the forehearth 10 below the level of the molten glass G are constructed of glass contact refractory.
A plurality of burner ports 18 is drilled through the sidewalls 16. The burner ports 18 are drilled through the super structure of the forehearth 10. The burner ports 18 are drilled at a right angle relative to the sidewalls 16. The burner ports 18 are adapted to receive burners 20. The burner ports 18 are spaced about four to five inches from one another. Consequently, a large number of burners, manifolds, pipes, fittings and valves (not shown) are associated with air-gas mixture burners.
In a conventional firing system, a source of air and a source of gas pass through regulators. The air and gas are mixed and then passed through a system of pipes to a plurality of burners, typically 20 to 100 burners. The burners are typically air-gas mixture burners which use the air as an oxidant for the combustion of the gas to provide heat to a zone, commonly referred to as a control zone. The front end typically has between six and sixty control zones, each complete with a gas control safety and pressure reduction system, combustion air blowers, and valves and regulators capable of controlling the temperature of the molten glass G between the melter and the forming position.
An air-gas mixture firing system is not only costly to construct, it is inefficient to operate. An air-gas mixture firing system uses 30 to 75 cubic feet per hour of gas to heat a one-foot section of channel with an air-gas mixture. It requires about 10 cubic feet of air for combustion of 1 cubic foot of natural gas. The air must be heated from an ambient temperature to the temperature of the exhaust gas stream. About 70 to 85 percent of the energy heats the air to the exhaust gas temperature, leaving 15 to 30 percent of the energy as heat available for the glass forming operation. Thus, an air-gas mixture firing system has minimum efficiency of combustion.
In addition to having a minimum efficiency of combustion, an air-gas mixture firing system is an inefficient means to heat the molten glass G. The flame temperature of an air-gas mixture burner in the air-gas mixture firing system reaches about 3500° F. However, the optical properties of the molten glass G and products of combustion limit the amount of radiant energy that penetrates the molten glass G. This causes the vertical temperature gradient of the molten glass G to be high. With air-gas burners it is difficult to control the temperature distribution in the glass by controlling the profile of the burners.
What is needed is a front end that reduces fuel consumption by using a low-cost system for firing forehearths with a combination of gas and oxygen.